<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>使用WebGL绘制一个点</title>
</head>

<body>
  <!--canvas标签创建一个宽高均为500像素，背景为蓝色的矩形画布-->
  <canvas id="webgl" width="500" height="500" style="background-color: grey"></canvas>


  <script>
    //通过getElementById()方法获取canvas画布
    var canvas = document.getElementById('webgl');
    //通过方法getContext()获取WebGL上下文
    var gl = canvas.getContext('webgl');

    //顶点着色器源码
    var vertexShaderSource = '' +
      'void main(){' +
      //给内置变量gl_PointSize赋值像素大小
      '   gl_PointSize = 30.0;' +
      //顶点位置，位于坐标原点
      '   gl_Position = vec4(0.0,0.0,0.0,1.0);' +
      '}';

    //片元着色器源码
    var fragShaderSource = '' +
      'void main(){' +
      //定义片元颜色
      '   gl_FragColor = vec4(0.6,0.0,0.0,1.0);' +
      '}';

    //初始化着色器
    var program = initShader(gl, vertexShaderSource, fragShaderSource);
    //开始绘制，显示器显示结果
    gl.drawArrays(gl.POINTS, 0, 1);

    //声明初始化着色器函数
    function initShader(gl, vertexShaderSource, fragmentShaderSource) {
      //创建顶点着色器对象
      var vertexShader = gl.createShader(gl.VERTEX_SHADER);
      //创建片元着色器对象
      var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
      //引入顶点、片元着色器源代码
      gl.shaderSource(vertexShader, vertexShaderSource);
      gl.shaderSource(fragmentShader, fragmentShaderSource);
      //编译顶点、片元着色器
      gl.compileShader(vertexShader);
      gl.compileShader(fragmentShader);

      //创建程序对象program
      var program = gl.createProgram();
      //附着顶点着色器和片元着色器到program
      gl.attachShader(program, vertexShader);
      gl.attachShader(program, fragmentShader);
      //链接program
      gl.linkProgram(program);
      //使用program
      gl.useProgram(program);
      //返回程序program对象
      return program;
    }
  </script>
</body>

</html>
